The purpose of this project is to determine the effects of light on model nucleic acids, and how alterations in chemical structure and conformation relate to modified biological activities (mutagenesis and carcinogenesis). Ribosyl- and deoxy- oligonucleotides of defined sequence are chemically synthesized. These nucleic acids contain normal and fluorinated bases. They are irradiated with different wavelengths of light, but concentrating on the ultraviolet-B region (280-320 nm). Various photosensitizers are used in the presence and absence of oxygen. The photoproducts which result are separated and purified in the intact nucleic acid using TLC and HPLC, and are structurally characterized using UV, mass spectrometry and NMR. The conformation of the various photoproducts are determined as well as the effects they transmit to neighboring regions of the normal nucleic acid using multi- nuclear magnetic resonance spectroscopy, x-ray crystallography, molecular modelling and energy minimization techniques.